L12: Regulation of eukaryote gene expression Flashcards
Stages where eukaryotic gene expression is regulated
1) Transcriptional regulation
2) mRNA processing
3) Regulation of mature mRNA
4) Translation
5) Post-translation
What roles do promoters and enhancers play in regulating gene expression?
Promoters initiate & regulate transcription; enhancers increase transcription rate
What is the function of DNA-binding transcription factors, such as the TATA Binding Protein?
They regulate gene expression by controlling transcription
What are histones and what role do they play in packaging chromatin?
Major structural proteins of chromatin & allow packaging of DNA into eukaryotic chromosomes
What is the difference between general transcription factors and tissue-specific transcription factors?
General transcription factors are required for basal transcription
Tssue-specific factors modulate transcription in certain cell types
What is the significance of cytosine methylation in gene regulation?
Promoting transcriptional repression
How does chromatin modification influence eukaryotic gene expression?
It alters the accessibility of DNA for transcription
How is eukaryotic gene expression regulated at the level of transcription?
Transcription factors binding to promoter regions
What is the role of regulatory transcription factors in gene expression?
To influence the rate of transcription
RNA polymerase in eukaryotes
Transcribe genes
Role of RNA polymerase I & III
Transcribe ribosomal RNAs, tRNAs & small nuclear RNAs
Role of RNA polymerase II
Transcribe protein-coding genes & some noncodinng RNAs
What does the eukaryotic promoter contain?
Binding site for RNA polymerase II & general transcription factors
What does these promotor sequences direct?
Direct RNA polymerase II to start transcription (starts at initiator region)
What does the regulatory region ot the promoter contain?
DNA sequence recognised by regulatory transcription factors
What are regulatory transcription factors?
Proteins that regulate whether transcription is initiated
What types of RNA polymerases are present in eukaryotes and what do they transcribe?
RNA polymerase I (rRNA)
RNA polymerase II (mRNA)
RNA polymerase III (tRNA)
How do eukaryotic cells respond to environmental conditions regarding gene expression?
By modifying gene expression mechanisms
Why do eukaryotes have greater regulation of gene expression compared to prokaryotes?
Eukaryotes have more complex cellular structures and regulatory sequences
What is the structure and function of a eukaryotic promoter?
A regulatory region of DNA that initiates gene transcription
How does the TATA binding protein binds DNA?
“Commitment factor” for transcription of mRNA
Binds DNA in minor groove and bends it, allowing other proteins (RNA polymerase) to recognise & bind promotor
How do transcription factors activate/repress transcription?
Interacting with pol II or general TFs
Folding of DNA
Creation of transcription complex
Acts to integrate activity of various TFs
How do enhancer sequences affect transcription in eukaryotic cells?
They increase transcription by binding transcription factors
2 motifs that display different DNA binding domains
1) Leucine zipper motif
2) Helix-loop-helix motif
Features of enhancer sequences
- Can be positioned upstream/downstream of promotors
- Contain multiple binding sites/tissue specific TF
- Can be close to transcription start site or 50kb away
What is a mediator?
A complex of proteins that links upstream-bound TFs to the basal complex
How does histone acetylation modify chromatin structure?
Relaxes chromatin, increasing gene expression
What is the pre-initiation complex and why is it important for transcription?
A complex that initiates eukaryotic transcription
What is the relationship between nucleosomes and chromatin structure?
Nucleosomes are the basic structural units that organize to form chromatin
How can alternative splicing produce different mRNA molecules from the same gene?
By using different combinations of exons
How do transcription factors interact with RNA polymerase II during transcription initiation?
They guide and stabilize RNA polymerase II at the promoter
What is the effect of DNA methylation on transcription factor binding?
Reduces transcription factor binding
What is the impact of post-translational modifications on protein function?
They alter protein folding, localization, and interactions
What are cis-acting regulatory sequences?
Bound by TFs to regulate transcription of genes on the same chromosome as the sequences
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What are trans-acting regulatory proteins?
Bind to their target sequences on any chromosome
What is the transcription factor MyoD?
Drives the expression of genes in muscles
What are open promotors?
Genes not packed into nucleosomes
What are covered promotors?
Regulated genes pakced into nucleosomes
What can chromatin be modified by?
Histone acetylation
How does histone aceylation modify chromatin?
Addition of acetyl groups to histones reduces +ve charge so histones bind DNA less tightly
- Acetyl group adds specific lysines
- This loosening of chromatin allows RNA pol II & TFs to bind to DNA
2 ways DNA can be modified
1) Histone acetylation
2) Methylation of cytosine
How can methylation of cytosine modify DNA?
Cytosine methylated at the 5C position
- This group protrudes into minor groove & affect TF binding & chromatin packing
Where are cytosins that are methylated found in?
CpG islands
What are CpG islands?
Stretches of sequence which include CG doublets- occur near promotors
